Sink drainboard



FIG. 1 is a perspective view of a sink drainboard showing our design;

FIG. 2 is a side elevation view of a first side;

FIG. 3 is a side elevation view of a second side;

FIG. 4 is a top plan view; and,

FIG. 5 is a bottom plan view.

The broken-line disclosures in the view represents portions of the sink drainboard in which the claimed design is embodied, but which forms no part of the claimed design. 

CLAIM The ornamental design for a sink drainboard, as shown and described. 